Reverse Combustion: Can CO2 Be Turned Back into
Fuel?

SOLAR FUELS: Using
this giant dish made of mirrors, Sandia scientists
concentrate sunlight on a specially designed
solar-fuel generator that can break down
CO2 and water.

Image: Photo by Randy Montoya / Sandia National
Laboratories

In the 1990s a graduate student named Lin Chao
at Princeton University decided to bubble carbon
dioxide into an electrochemical cell. Using cathodes
made from the element palladium and a catalyst
known as pyridinium—a garden variety organic
chemical that is a by-product of oil refining—he
discovered that applying an electric current would
assemble methanol from the CO2. He published his
findings in 1994—and no one cared.

But by 2003, Chao's successor in the Princeton
lab of chemist Andrew Bocarsly was deeply interested
in finding a solution to the growing problem of
the CO2 pollution causing global climate change.
Graduate student Emily Barton picked up where he
left off and, using an electrochemical cell that
employs a semiconducting material used in photovoltaic
solar cells for one of its electrodes, succeeded
in tapping sunlight to transform CO2 into the basic
fuel.

"The dominant thinking 10 years ago was that
we should bury the CO2. But if you could efficiently
convert it into something that we wouldn't have
to spend all that money and energy to put into
the ground, sort of recycle it, that would be better," Bocarsly
says. "We take CO2, water, sunlight and an
appropriate catalyst and generate an alcoholic
fuel."

He adds: "We didn't have some brilliant insight
here. We had some luck." Luck that venture
capitalists are now trying to turn into cash flow
via a start-up known as Liquid Light.

Turning CO2 into fuels is exactly what photosynthetic
organisms have been doing for billions of years,
although their fuels tend to be foods, like sugars.
Now humans are trying to store the energy in sunlight
by making a liquid fuel from CO2 and hydrogen—a
prospect that could recycle CO2 emissions and slow
down the rapid buildup of such greenhouse gases
in the atmosphere. "You take electricity and
combine CO2 with hydrogen to make gasoline," explained
Arun Majumdar, director of the Advanced Research
Projects Agency–Energy (ARPA–e) that
is pursuing such technology, at a conference in
March. "This is like killing four birds with
one stone"—namely, energy security,
climate change, the federal deficit and, potentially,
unemployment.

"When these new technologies get commercialized,
those jobs always end up in the U.S.," argues
chemical engineer Alan Weimer of the University
of Colorado at Boulder, who is working on such
solar-fuel generators. Adds chemist Michael Berman
of the U.S. Air Force Office of Scientific Research,
which is funding research into the possibilities
of solar fuels, including Bocarsly's work: "The
country, and the Air Force, need secure and sustainable
sources of energy…. Since the sun provides
enough energy for our needs, our goal is to make
a fuel using CO2 and sunlight—and maybe water—as
feedstocks to produce the chemical fuel that can
store the sun's energy in a form that we can use
where and when we need.